DE68924950T2 - Electrophotographic photoreceptor. - Google Patents

Description

The present invention relates to an electrophotographic photoreceptor, and more particularly to an electrophotographic photoreceptor having excellent electrostatic properties and excellent moisture resistance, and particularly excellent performance characteristics as a CPC photoreceptor.

Depending on the required properties or the electrophotographic process to be used, an electrophotographic photoreceptor can have a variety of structures.

A system is widely used in which a photoreceptor comprises a support having thereon at least one photoconductive layer and, if necessary, an insulating layer on the surface thereof. The photoreceptor comprising a support and at least one photoconductive layer is subjected to ordinary electrophotographic processing for image formation, including charging, imagewise exposure, development and, if desired, transfer.

Electrophotographic photoreceptors have also been widely used as offset plate precursors for direct plate making. In particular, a direct electrophotographic planographic printing system has recently gained greater importance as a system that provides hundreds to thousands of prints of high image quality.

Binders used in the photoconductive layer should themselves have film-forming properties and the ability to disperse photoconductive particles therein. When formulated into a photoconductive layer, the binders should also have satisfactory adhesion to the support. They must also have diverse electrostatic properties and image-forming properties such that the photoconductive layer exhibits excellent electrostatic capacity, low decay in the dark and high decay in the light, undergoes practically no fatigue before exposure, and maintains these properties in a stable manner against changes in humidity at the time of image formation.

Binder resins that have been conventionally used include silicone resins (see JP-B-34-6670, the term "JP-B" as used herein means an "examined published Japanese patent application"), styrene-butadiene resins (see JP-B-35-1960), alkyd resins, maleic acid resins and polyamides (see Japanese JP-B-35-11219), vinyl acetate resins (see JP-B-41-2425), vinyl acetate copolymer resins (see JP-B-41-2426), acrylic resins (see JP-B-35-11216), acrylic ester copolymer resins (see JP-B-35-12129, JP-B-36-81510 and JP-B-41-13946), etc. However, the electrophotographic photosensitive materials using these known resins have a number of disadvantages, i.e., poor affinity to photoconductive particles (poor dispersion of a photoconductive coating composition); poor charging properties of the photoconductive layer; poor quality of the reproduced image, particularly dot reproducibility or resolving power; susceptibility of the quality of the reproduced image to environmental influences at the time of electrophotographic image formation such as high temperature and high humidity or low temperature and low humidity conditions; and the like.

In order to improve the electrostatic properties of a photoconductive layer, various approaches have been taken heretofore. For example, incorporation of a compound containing an aromatic ring or furan ring containing a carboxyl group or a nitro group, either alone or in combination with a dicarboxylic acid anhydride, into a photoconductive layer has been proposed as disclosed in JP-B-42-6878 and JP-B-45-3073. However, the photosensitive materials thus improved still have insufficient electrostatic properties, particularly light decay properties. The insufficient sensitivity of these photosensitive materials has been compensated by incorporating a large amount of a sensitizing dye into the photoconductive layer. However, photosensitive materials containing a large amount of a sensitizing dye undergo considerable deterioration in whiteness, which means reduced quality as a recording medium, occasionally causing deterioration in decay properties in the Darkening, which prevents a satisfactory reproduced image from being obtained.

On the other hand, JP-A-60-10254 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes to control the average molecular weight of a resin to be used as a binder of the photoconductive layer. According to this proposal, the combined use of an acrylic resin having an acid value of 4 to 50 whose average molecular weight is distributed within two ranges, i.e., a range of 1 x 10³ to 1 x 10⁴ and a range of 1 x 10⁴ and 2 x 10⁵ improves electrostatic properties, particularly reproducibility as a PPC photoreceptor in repeated use, moisture resistance, and the like.

In the field of planographic printing plate precursors, extensive studies have been made to provide binder resins for a photoconductive layer having electrostatic properties compatible with printing properties. Examples of binder resins which have been reported heretofore to be effective for oil desensitization of a photoconductive layer include a resin having a molecular weight of 1.8 x 10⁴ to 10 x 10⁴ and a glass transition point of 10°C to 80°C obtained by copolymerizing a (meth)acrylate monomer and a copolymerizable monomer in the presence of fumaric acid in combination with a copolymer of a (meth)acrylate monomer and a copolymerizable monomer other than fumaric acid as disclosed in JP-B-50-31011; a terpolymer containing a (meth)acrylic acid ester unit having a substituent having a carboxyl group at a distance of at least 7 atoms from the ester bond as disclosed in JP-A-53-54027; a tetra- or penta-polymer containing an acrylic acid unit and a hydroxyethyl (meth)acrylate unit as disclosed in JP-A-54-20735 and JP-A-57-202544; a terpolymer containing a (meth)acrylic acid ester unit having an alkyl group having 6 to 12 carbon atoms as a substituent and a vinyl monomer containing a carboxyl group as disclosed in JP-A-58-68046; and the like.

However, none of these proposed resins has been found to be satisfactory for practical use in terms of charging properties, charge retention in the dark, photosensitivity and surface smoothness of the photoconductive layer.

The binder resins proposed for use in precursors for electrophotographic planographic printing plates have been found, in actual evaluation, to give rise to problems with respect to electrostatic properties, staining in the background of prints and moisture resistance.

Electrophotographic recording systems using a laser beam as a light source have been developed recently. In this system, laser light emitted from a laser and condensed by an fθ lens is reflected on a polygonal mirror to form a scanning image on a photoreceptor, and the image is then developed and transferred if necessary.

With the recent development of low-power semiconductor lasers, e.g., about 4 mW to 25 mW, the development of a photosensitive material having a sensitivity in the wavelength range of 700 nm or more is increasingly required. An electrophotographic photoreceptor that is applicable to processing using such a low-power laser must have special properties different from those required for conventional electrophotographic photoreceptors. Particularly important is the property that the photoreceptor should exhibit sufficient sensitivity to light in the near infrared to infrared range and also satisfactory charge retention in the dark.

It is known to combine a dispersed system of photoconductive substance-binder-resin with various kinds of near infrared to infrared spectral sensitizing dyes to form an electrophotographic photoreceptor, as disclosed in JP-A-58-58554, JP-A-58-42055, JP-A-58-59453 and JP-A-57-46245. However, it has been found that these photoreceptors have insufficient charge retention in the dark and insufficient photosensitivity. As stated above, when a laser such as a semiconductor laser is used as a light source, the exposure of the photoconductive layer is effected by scanning, so that the time from charging to the end of exposure becomes longer than that required in the conventional exposure of visible light over the entire surface thereof. The charge on the non-exposed area should be sufficiently retained over this time. Thus, charge retention in the dark is one of the extremely important properties required for electrophotographic photoreceptors to be used in scanning exposure. The conventional photoreceptors described above have not been satisfactory in this respect.

Considering the low power of the light source, a sufficiently high sensitivity in the range from near infrared to infrared is also an important property. Conventional photoreceptors are also unsatisfactory in this respect.

An object of the present invention is to provide an electrophotographic photoreceptor having improved electrostatic properties, particularly charge retention in the dark and photosensitivity, and improved image reproducibility.

Another object of the invention is to provide an electrophotographic photoreceptor which can produce a clear reproduced image of high quality which is not affected by variations in the environmental conditions at the time of image reproduction, such as a change to low temperature and low humidity conditions or to high temperature and high humidity conditions.

Another object of the present invention is to provide an electrophotographic CPC photoreceptor having excellent electrostatic properties and a small change due to environmental changes.

Still another object of the present invention is to provide an electrophotographic photoreceptor which provides a clear reproduced image of high quality even when processed by a scanning exposure system using a semiconductor laser beam.

Still another object of the present invention is to provide a planographic printing plate precursor which provides a planographic printing plate in which no background stains occur.

A still further object of the present invention is to provide an electrophotographic photoreceptor which is hardly influenced by the kind of sensitizing dyes used in combination therewith.

It has now been found that the above objects of the present invention can be achieved by an electrophotographic photoreceptor comprising a support having thereon at least one photoconductive layer containing at least inorganic photoconductive particles and a binder resin, said binder resin having a weight average molecular weight of 1 x 10³ to 5 x 10⁴ and comprising (A) at least one resin containing as a polymerization component not less than 30% by weight of at least one repeating unit (ai) represented by the formula (I) or (II):

wherein X₁ and X, which may be the same or different, each represent a hydrogen atom, a hydrocarbon group having 1 to 10 carbon atoms, a chlorine atom, a bromine atom, -COY₁ or -COOY, Y₁ and Y each represent a hydrocarbon group having 1 to 10 carbon atoms, with the proviso that X₁ and X cannot both represent hydrogen at the same time; and W₁ and W each represent a bond or a linking group containing 1 to 4 linking atoms connecting -COO- and the benzene ring, wherein at least one acidic group selected from the group consisting of

(i) -PO₃H, (ii) SO₃H, (iii) -COOH,

wherein R represents a hydrocarbon group having 1 to 10 carbon atoms or -OR', wherein R' represents a hydrocarbon group having 1 to 10 carbon atoms, and (v) a cyclic acid anhydride containing group bonded to only one of the ends of the polymer main chain thereof.

The term "hydrocarbon group" as used herein means an alkyl group, an alkenyl group, an aralkyl group, or an aryl group.

It has also been found that the film strength of a photoconductive layer can be further improved to provide an electrophotographic photoreceptor exhibiting excellent printing durability by using the above-mentioned resin (A) further comprising 1 to 20% by weight of at least one repeating unit (a-ii) containing a heat- and/or photo-curing functional group.

It has further been found that the improvement in film strength can be enhanced by using as the binder resin (B) at least one resin having a weight average molecular weight of 2 x 10⁴ to 6 x 10⁵ in combination with the resin (A).

In a preferred embodiment, the resin (B) comprises at least 30% by weight of a repeating unit (bi) represented by the formula (III):

wherein a1 and a, which may be the same or different, each represents a hydrogen atom, a halogen atom, a cyano group or a hydrocarbon group; and R0 represents a hydrocarbon group.

The resin (B) preferably contains, in addition to the repeating unit (b-i), 0.05 to 5% by weight of a copolymerization component containing the acidic group (a-i) as described above, and has a weight average molecular weight of 2 x 10⁴ to 1 x 10⁵.

In a further preferred embodiment, the resin (B) contains 1 to 30 weight percent of at least one repeating unit containing a heat- and/or light-curing functional group.

The electrophotographic photoreceptor of the present invention preferably contains a heat- and/or light-curing crosslinking agent in combination with the binder resin.

The resin (A) which can be used as a binder in the present invention has a weight average molecular weight of 1 x 10³ to 2 x 10⁴, preferably 3 x 10³ to 1 x 10⁴. The resin (A) contains not less than 30% by weight, more preferably 50 to 97% by weight, of a copolymerization component (ai) corresponding to the repeating unit represented by formulas (I) and (II). The proportion of the copolymerization component containing the above-mentioned acidic group in the resin (A) is 0.5 to 15% by weight, more preferably 3 to 10% by weight. The proportion of the copolymerization component (a-ii) containing a heat- and/or light-curing functional group, when present, is 1 to 30% by weight. The resin (A) preferably has a glass transition point (Tg) of -10 to 100°C, more preferably -5 to 80°C.

If the molecular weight of the resin (A) is less than 1 x 10³, the film-forming properties of the binder are reduced and sufficient film strength is not maintained. On the other hand, the electrophotographic properties, and in particular the initial potential and dark decay retention, deteriorate if it exceeds 2 x 10⁴. The deterioration of the electrophotographic properties is particularly pronounced when such a high molecular weight polymer having an acidic group-containing copolymerization component content exceeding 3% is used, resulting in considerable background staining when used as an offset stencil.

If the resin (A) contains less than 0.5% by weight of the acidic group-containing copolymerization component, the initial potential for obtaining a sufficient image density is too low. If the content exceeds 15% by weight, the dispersibility is reduced, the film smoothness and the moisture resistance are deteriorated, and background stains are increased when the photoreceptor is used as an offset stencil.

When the resin (A) contains a heat- and/or light-curing functional group, an improvement in the film strength of a photoconductive layer is not brought about due to an insufficient curing reaction if the content of this copolymerization component is less than 1% by weight. On the other hand, more than 30% by weight of this component deteriorates the excellent electrophotographic properties brought about by the resin (A), resulting only in properties obtained by using the conventionally known binder resins. In addition, an offset master plate made from the resulting photoreceptor has considerable background stains in prints.

The resin (B) which can be used in the present invention suitably has a weight average molecular weight of 2 x 10⁴ to 6 x 10⁵. When the resin (B) does not contain, as a polymerization component, a component containing the specific acidic group present in the resin (A) or a component containing a heat- and/or light-curing functional group (i.e., a-ii), a preferable weight average molecular weight of this resin (B) is 8 x 10⁴ to 6 x 10⁵. When it contains the specific acidic group-containing component and/or the heat- and/or light-curing functional group-containing component, a preferable weight average molecular weight of this resin (B) is 2 x 10⁴ to 1 x 10⁵.

If the weight average molecular weight of the resin (B) containing neither the acidic group-containing component nor the curing functional group-containing components is less than 8 x 10⁴, the effect of improving the film strength becomes insufficient and the printing durability of a produced offset master plate is insufficient for obtaining more than 10,000 prints. On the other hand, if it exceeds 6 x 10⁵, the resin (B) has a reduced solubility in organic solvents and as a result, uniform dispersion of the photoconductive substance can hardly be obtained, and this leads to a reduced film strength.

If the weight average molecular weight of the resin (B) containing an acidic group-containing component and/or a curing functional group-containing component is less than 2 x 10⁴, sufficient film strength for use as an offset master plate precursor is not obtained. If it exceeds 1 x 10⁵, the dispersion tends to form agglomerates or the resulting photoconductive layer tends to become brittle because the film hardness is too high, ultimately resulting in reduced film strength. Moreover, the electrophotographic properties of the resulting photoreceptor are considerably reduced, particularly in dark decay retention and photosensitivity.

If desired, a crosslinking agent may be used in combination with the binder resin. The crosslinking agent is preferably used in an amount of 1 to 30% by weight, more preferably 5 to 20% by weight, based on the weight of the entire binder resin. Use of less than 1% by weight of the crosslinking agent produces no effect in improving film strength. Use of more than 30% by weight of the crosslinking agent results in deterioration of electrophotographic properties such as initial potential, dark decay retention, photosensitivity and residual potential. Further, an offset master plate prepared using such a large amount of a crosslinking agent has considerable background stains.

As described above, conventionally known acidic group-containing binder resins have been mainly proposed for use in an offset master plate and therefore have a high molecular weight, e.g., more than 5 x 10⁴, in order to maintain film strength and thereby improve printing durability.

On the other hand, in the acidic group-containing resin (A) having a methacrylate copolymerization component having a specific substituent, it was confirmed that the methacrylate component containing a planar benzene ring or naphthalene ring and the acidic group are suitably adsorbed to stoichiometric defects of an inorganic photoconductive substance and the surface thereof is sufficiently covered. Thus, the electron traps of the photoconductive substance can be compensated and the moisture resistance can be greatly improved while promoting sufficient dispersion of the photoconductive particles without agglomeration. The fact that the resin (A) has a low molecular weight also improves the covering ability for the surface of the photoconductive particles.

The photoconductive layer obtained by the present invention has an improved surface smoothness. When a photoreceptor to be used as a planographic printing plate precursor is prepared from a non-uniform dispersion of the photoconductive particles in a binder resin having agglomerates present therein, is used, the photoconductive layer has a rough surface. As a result, non-image areas cannot be made uniformly hydrophilic by oil desensitization treatment with an oil desensitizing solution. Under these circumstances, the resulting printing plate induces adhesion of a printing ink to the non-image areas during printing, resulting in background stains in the non-image areas of prints.

Thus, the low molecular weight resin (A) of the present invention is sufficiently adsorbed on the photoconductive particles to cover the surface of the particles, thereby providing smoothness of the photoconductive layer, satisfactory electrostatic properties and stain-free images. The film strength of the resulting photoreceptor is sufficient for use as a CPC photoreceptor or as an offset printing plate precursor for the preparation of an offset printing plate to be used for obtaining about a thousand prints under limited printing conditions such as printing by means of a desktop (small-sized) printer.

In addition, it has been proved that the mechanical strength of the photoconductive layer can be further improved by various embodiments of the present invention. That is, an improvement in film strength can be achieved by (1) an embodiment in which the resin (A) further contains a curing functional group and/or a curing functional group-containing resin (A) is combined with a curing functional group-containing resin (B) and/or a crosslinking agent to thereby induce crosslinking between the resin (A) and/or between the resins (A) and (B); (2) an embodiment in which the resin (A) not containing a curing functional group is combined with a high molecular weight resin (B), thereby making use of the advantage of entanglement of the long high molecular weight chains of the resin (B) per se; (3) an embodiment in which the resin (A) is combined with resin (B) containing a small amount of a specific acidic group to thereby cause the resin (B) to exert a weak mutual action on the inorganic photoconductive particles; (4) an embodiment in which in which resin (A) is combined with resins (B) containing a curing functional group and a crosslinking agent to induce a crosslinking reaction between the molecules of resin (B); and (5) an embodiment in which resin (A) is combined with resin (B) containing both an acidic group-containing component and a curing functional group-containing component, thereby producing the two effects described above.

Improved mechanical strength of the photoconductive layer as obtained in these preferred embodiments results in not only improved performance properties for use as a CPC photoreceptor, such as abrasion resistance, writability and filing properties (strength can be maintained during filing), but also improved performance properties for use as a precursor for an offset master plate, such as a printing durability amounting to 6,000 to 10,000 prints regardless of variations in printing conditions (e.g., use of a large-sized printing device or increased printing pressure). In other words, these preferred embodiments provide an improvement in the mechanical strength of the photoconductive layer which, depending on the end use, might be insufficient when using resin (A) alone, without in any way affecting the function of resin (A).

The electrophotographic photoreceptor of the present invention thus has excellent electrostatic properties regardless of variations in environmental conditions as well as sufficient film strength, thereby making it possible to provide an offset master plate having a printing durability of more than 10,000 prints. Furthermore, these excellent electrostatic properties can be stably obtained regardless of environmental conditions even when processed according to a scanning exposure system using a semiconductor laser beam.

The repeating unit (a-i) constituting at least 30% by weight of the resin (A) can be represented by the formula (I) or (II).

In formula (I), X₁ and X each preferably represent a hydrogen atom, a chlorine atom, a bromine atom, an alkyl group having up to 4 carbon atoms (e.g. methyl, ethyl, propyl and butyl), an aralkyl group having 7 to 9 carbon atoms (e.g. benzyl, phenethyl, 3-phenylpropyl, chlorobenzyl, dichlorobenzyl, bromobenzyl, methylbenzyl, methoxybenzyl and chloromethylbenzyl), an aryl group (e.g. phenyl, tolyl, xylyl, bromophenyl, methoxyphenyl, chlorophenyl and dichlorophenyl) or -COY₁ or -COOY, wherein Y₁ and Y each preferably represent any of the above-mentioned hydrocarbon groups, with the proviso that X₁ and X do not simultaneously represent a hydrogen atom.

In formula (I), W1 is a bond or a linking group containing 1 to 4 connecting atoms connecting -COO- and the benzene ring, e.g. (-CH-)n (n: 1, 2 or 3), -CHCHOCO-, (-CH-)m (m: 1 or 2) and -CHCHO-.

In formula (II), W has the same meaning as W₁.

The proportion of the polymerization or copolymerization component corresponding to the repeating unit (a-i) in resin (A) is 30 to 100% by weight, preferably 60 to 100% by weight.

Concrete examples of repeating units (ai) represented by formula (I) or (II) are shown below for illustrative purposes, but the present invention should not be construed as being limited thereto.

The acidic group bonded to only one end of the polymer main chain in resin (A) includes -PO₃H, -SO₃H, -COOH,

or a cyclic acid anhydride-containing group.

In the group

R represents a hydrocarbon group or OR', where R' represents a hydrocarbon group. The hydrocarbon group represented by R or R' preferably includes an aliphatic group having 1 to 10 carbon atoms (e.g., methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl, octadecyl, 2-chloroethyl, 2-methoxyethyl, 3-ethoxypropyl, allyl, crotonyl, butenyl, cyclohexyl, benzyl, phenethyl, 3-phenylpropyl, methylbenzyl, chlorobenzyl, fluorobenzyl and methoxybenzyl) and a substituted or unsubstituted aryl group (e.g., phenyl, tolyl, ethylphenyl, propylphenyl, chlorophenyl, fluorophenyl, bromophenyl, chloromethylphenyl, dichlorophenyl, methoxyphenyl, cyanophenyl, acetamidophenyl, acetylphenyl and butoxyphenyl).

The cyclic acid anhydride-containing group is a group that contains at least one cyclic acid anhydride unit. The cyclic acid anhydride that is present includes aliphatic dicarboxylic acid anhydrides and aromatic dicarboxylic acid anhydrides.

Specific examples of aliphatic dicarboxylic anhydride rings include a succinic anhydride ring, a glutaconic anhydride ring, a maleic anhydride ring, a cyclopentane-1,2-dicarboxylic anhydride ring, a cyclohexane-1,2-dicarboxylic anhydride ring, a cyclohexene-1,2-dicarboxylic anhydride ring, and a 2,3-bicyclo[2.2.2]octanedicarboxylic anhydride ring. These rings may be substituted with, for example, a halogen atom (e.g., chlorine and bromine) and an alkyl group (e.g., methyl, ethyl, butyl, and hexyl).

Specific examples of aromatic dicarboxylic anhydride rings are a phthalic anhydride ring, a naphthalenedicarboxylic anhydride ring, a pyridinedicarboxylic anhydride ring and a thiophenedicarboxylic anhydride ring. These rings can be substituted with, for example, a halogen atom (e.g. chlorine and bromine), an alkyl group (e.g. methyl, ethyl, propyl and butyl), a hydroxyl group, a cyano group, a nitro group and an alkoxycarbonyl group (e.g. methoxycarbonyl and ethoxycarbonyl).

The resin (A) can be synthesized so that the specific acidic group can be bonded to a terminal of the main chain of the polymer comprising at least the polymerization component (a-i). More specifically, the resin (A) can be produced by a method using a polymerization initiator containing the specific acidic group or a functional group capable of being converted to the acidic group, a method using a chain transfer agent containing the specific acidic group or a functional group capable of being converted to the acidic group, a method using both the polymerization initiator and the chain transfer agent, and a method using the above functional group by taking advantage of the reaction termination in the anionic polymerization. Reference can be made, for example, to P. Dreyfuss and R.P. Quirk, Encyclo. Polym. Sci. Eng., No. 7, p. 551 (1987), V. Percec, Appl. Polymer. Sci., Volume 285, p. 95 (1985), P.F. Rempp and E. Franta, Adv. Polym. Sci., Vol. 58, p. 1 (1984), Y. Yamashita, J. Appl. Polymer. Sci. Appl. Polymer. Symp., vol. 36, p. 193 (1981) and R. Asami and M. Takaki, Macromol. Chem. Suppl., Volume 12, p. 163 (1985).

In the repeating unit (a-ii) which preferably constitutes the resin (A), the term "heat- and/or light-curing functional group" means a functional group capable of initiating a resin curing reaction upon exposure to heat and/or light.

The proportion of the copolymerization component containing the heat- and/or light-curing functional group in the resin (A) is up to 20% by weight, preferably 1 to 20% by weight. If it is below If the amount of the film is less than 1% by weight, no noticeable effect in improving the film strength is produced due to insufficient hardening reaction. If it is more than 20% by weight, the film becomes so hard that the electrophotographic properties are reduced and the offset stencil produced therefrom suffers from increased staining.

Specific examples of light-curing functional groups are those employed in conventional photosensitive resins known as light-curable resins as described in Hideo Inui and Gentaro Nagamatsu, Kankosei Kobunshi, Kodansha (1977), Takahiro Tsunoda, Shin-kankosei Jushi, Insatsu Gakkai Shuppanbu (1981), GE. Green and B.P. Starch, J. Macro. Sci. Reas. Macro. Chem., C21 (2), pp. 187 - 273 (1981 - 1982), and C.G. Rattey, Photopolymerization of Surface Coatings, A. Wiley Interscience Pub. (1982).

The thermosetting functional group includes functional groups except for the acidic groups specified above. Examples of thermosetting functional groups are described, for example, in Tsuyoshi Endo, Netsukokasei Kobunshi no Seimitsuka, C.M.C. (1987), Yuji Harasaki, Saishin Binder Gilutsu Binran, Chapter II-I, Sogo Gijutsu Center (1985), Takayuki Ohtsu, Acryl Jushi no Gosei Sekkei to Shinyoto, Chubu Kei-ei Kaihatsu Center Shuppanbu (1985), and Eizo Ohmori, Kinosei Acryl Jushi, Techno System (1985).

Concrete examples of curing functional groups are -OH, -SH, -NH, -NHR₁₁ (where R₁₁ is a hydrocarbon group such as a substituted or unsubstituted alkyl group (e.g. methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, 2-chloroethyl, 2-methoxyethyl and 2-cyanoethyl), a substituted or unsubstituted cycloalkyl group having 4 to 8 carbon atoms (e.g. cycloheptyl and cyclohexyl), a substituted or unsubstituted aralkyl group having 7 to 12 carbon atoms (e.g. benzyl, phenethyl, 3-phenylpropyl, chlorobenzyl, methylbenzyl and methoxybenzyl) and a substituted or unsubstituted aryl group (e.g. phenyl, tolyl, xylyl, chlorophenyl, bromophenyl, methoxybenzyl and naphthyl),

-CONHCHOR₁₂ (wherein R₁₂ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms (e.g. methyl, ethyl, propyl, butyl, hexyl and octyl)), -N=C=O and a group having a polymerizable double bond

(wherein a₁₁ and a₁₂ each represent a hydrogen atom, a halogen atom (e.g. chlorine and bromine) or an alkyl group having 1 to 4 carbon atoms (e.g. methyl and ethyl)). Concrete examples of the group containing the polymerizable double bond include

and CH-CH-S-.

The incorporation of the above-described curing functional group can be carried out by a method of introducing the functional group into a polymer by means of a high polymer reaction or a method of copolymerizing a monomer containing one or more of these functional groups and a monomer corresponding to the repeating unit (a-i).

The high polymer reaction can be carried out using known methods of low molecular weight synthesis. Reference can be made, for example, to Nippon Kagakukai (ed.), Shin Jikken Kagaku Koza, Volume 14, "Yuki Kagobutsu no Gosei to Han-no (I) - (V)", Maruzen K.K., and Yoshio Iwakura and Keisuke Kurita, Han-nosei Koibunshi.

The monomer containing one or more light- and/or heat-curing functional groups includes vinyl compounds which are copolymerizable with the monomer corresponding to the repeating unit (a-i) and which contain the functional group. Examples of such vinyl compounds are described, for example, in Kobunshi Gakkai (ed.), Kobunshi Data Handbook (Kisohen), Baihukan (1986). Specific examples of these vinyl monomers are acrylic acid, α- and/or β-substituted acrylic acids (e.g. α-acetoxy-, α-acetoxymethyl-, α-(2-amino)methyl-, α-chloro-, α-bromo-, α-fluoro-, α-tributylsilyl-, α-cyano-, β-chloro-, β-bromo-, α-chloro-β-methoxy- and α,β-dichloro compounds), methacrylic acid, itaconic acid, itaconic acid half-esters, itaconic acid half-amides, crotonic acid, 2-alkenylcarboxylic acids (e.g. 2-pentenoic acid, 2-methyl-2-hexenoic acid and 4-ethyl-2-octenoic acid), maleic acid, maleic acid half-esters, maleic acid half-amides, vinylbenzenecarboxylic acid, vinylbenzenesulfonic acid, vinylsulfonic acid, vinylphosphonic acid, vinyl or allyl half-ester derivatives of dicarboxylic acids and ester or amide derivatives of these carboxylic acids or sulfonic acids containing the acidic group in the substituents thereof.

Concrete examples of the heat- and/or light-curing functional group-containing repeating unit (a-ii) are shown below. (as in the following) integer from 1 to 11 integer of integer of C₁-C₄ alkyl group

The resin (A) may further comprise other copolymerizable monomers in addition to the monomer corresponding to the repeating unit of formula (I) or (II) and, if desired, the heat- and/or photocurable functional group-containing monomer. Examples of such monomers include unsaturated carboxylic acid esters such as methacrylic acid esters, acrylic acid esters, crotonic acid esters and itaconic acid diesters (the ester groups of these unsaturated carboxylic acids include methyl, ethyl, propyl, butyl, heptyl, hexyl, octyl, decyl, dodecyl, 2-hydroxyethyl, 2-chloroethyl, 2-methoxyethyl, methoxymethyl, ethoxymethyl, 2,3-dihydroxypropyl, 2-(N,N-dimethylamino)ethyl, 2-(N-morpholino)ethyl, 2-furylethyl, benzyl, phenethyl, cyclohexyl and phenyl groups), α-olefins, vinyl alkanoates, allyl alkanoates, acrylonitrile, methacrylamides, styrenes and heterocyclic Vinyl compounds (e.g. vinylpyrrolidone, vinylpyridine, vinylimidazole, vinylthiophene, vinylimidazoline, vinylpyrazoles, vinyldioxane, vinylquinoline, vinylthiazoles and vinyloxazine).

As the resin (B), any of the binder resins conventionally used in electrophotographic photoreceptors can be used as long as the molecular weight condition is satisfied. The resin (B) can be used either singly or as a combination of two or more of them. Specific examples of usable resins (B) are described in Harumi Miyahara and Hidehiko Takei, Imaging, Vol. 1978, No. 8, pp. 9-12, and Takaharu Kurita and Jiro Ishiwatari, Kobunshi, Vol. 17, pp. 278-284 (1968).

Specific examples of resin (B) include olefin polymers and copolymers, vinyl chloride copolymers, vinylidene chloride copolymers, vinyl alkanoate polymers and copolymers, allyl alkanoate polymers and copolymers, polymers and copolymers of styrene derivative or derivatives thereof, butadiene-styrene copolymers, isoprene-styrene copolymers, butadiene-unsaturated carboxylic acid ester copolymers, acrylonitrile copolymers, methacrylonitrile copolymers, alkyl vinyl ether copolymers, acrylic acid ester polymers or copolymers, methacrylic acid ester polymers or copolymers, styrene-acrylic acid ester copolymers, styrene-methacrylic acid ester copolymers, itaconic acid diester polymers or copolymers, maleic anhydride copolymers, Acrylamide copolymers, methacrylamide copolymers, hydroxyl-modified silicone resins, polycarbonate resins, ketone resins, amide resins, hydroxyl- and carboxyl-modified polyester resins, butyral resins, polyvinyl acetal resins, cyclized rubber-methacrylic acid ester copolymers, cyclized rubber-acrylic acid ester copolymers, copolymers containing a heterocyclic ring containing no nitrogen atom (wherein the heterocyclic ring includes furan, tetrahydrofuran, thiophene, dioxane, dioxolane, lactone, benzofuran, benzothiophene and 1,3-dioxetane rings) and epoxy resins.

In one embodiment, the resin (B) preferably includes (meth)acrylate polymers or copolymers containing not less than 30% by weight of a (meth)acrylic acid ester unit represented by the formula (III):

wherein a1 and a, which may be the same or different, each represent a hydrogen atom, a halogen atom (chlorine atom and bromine atom), a cyano group or an alkyl group having 1 to 4 carbon atoms; and R0 a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms (e.g. methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl, tridecyl, tetradecyl, 2-methoxyethyl and 2-ethoxyethyl), a substituted or unsubstituted alkenyl group having 2 to 18 carbon atoms (e.g. vinyl, allyl, isopropenyl, butenyl, hexenyl, heptenyl and octenyl), a substituted or unsubstituted aralkyl group having 7 to 12 carbon atoms (e.g. benzyl, phenethyl, methoxybenzyl, ethoxybenzyl and methylbenzyl), a substituted or unsubstituted cycloalkyl group having 5 to 8 carbon atoms (e.g. cyclopentyl, cyclohexyl and cycloheptyl) and an aryl group (e.g. phenyl, tolyl, xylyl, mesityl, naphthyl, methoxyphenyl, ethoxyphenyl, chlorophenyl, dichlorophenyl, bromophenyl, chloromethylphenyl, bromochlorophenyl, butylphenyl, methoxycarbonylphenyl, phenoxyphenyl and cyanophenyl).

The preferred resin (B) described above is particularly advantageous in that an offset master plate made from the resulting photoreceptor has no background stains when printed.

In formula (III), a1 and a each preferably represent a hydrogen atom or a methyl group.

When a1 and a both represent a hydrogen atom and R0 represents an alkyl group having 6 to 18 carbon atoms, the proportion of such a component in the resin (B) is preferably not more than 60% by weight.

In this embodiment, the resin (B) preferably includes a random copolymer containing, in addition to the polymerization component (b-i) of the formula (III), 0.05 to 5% by weight of a copolymerization component containing the above-mentioned acidic group.

The polymerization component containing the specific acidic group may be any compound copolymerizable with the monomer corresponding to the polymerization component of the formula (III). Examples of usable compounds are those described above with respect to the resin (A).

In this embodiment, it is important that the resin (B) containing the acidic group-containing copolymerization component has a weight average molecular weight of not more than 1 x 10⁵. It is particularly preferred that the content of the acidic group-containing component in the resin (B) is in the range of 1 to 60% by weight of that in the resin (A).

In another embodiment, the resin (B) is preferably a copolymer containing 1 to 30% by weight of at least one component containing a heat- and/or photo-curable functional group. The heat- and/or photo-curable functional group referred to herein includes those described above with respect to the repeating unit (a-ii) of the resin (A).

The component copolymerizable with the unsaturated carboxylic acid ester includes not only monomers corresponding to the repeating unit of the formula (III), but also monomers such as α-olefins, vinyl alkanoates, allyl alkanoates, acrylonitrile, methacrylonitrile, vinyl ethers, acrylamides, methacrylamides, styrenes (e.g. styrene, vinyltoluene, vinylnaphthalene, butylstyrene, methoxystyrene, chlorostyrene, dichlorostyrene and bromostyrene), heterocyclic vinyl compounds (e.g. vinylpyrrolidone, pyridine, vinylimidazole, vinylthiophene, vinylimidazoline, vinylpyrazole, vinyldioxane, vinylquinoline, vinylthiazole and vinyloxazine); compounds described in Kobunshi Gakkai (ed.), Kobunshi Data Handbook (Kosohen), 5. 175 - 181, DA Tomalia, Reactive Heterocyclic Monomers, Chapter 1 of "Functional Monomers Vol. 2", Marcel Dekker Inc., NY (1974), and LS Luskin, Basic Monomers, Chapter 3 of "Functional Monomers Vol. 2", Marcel Dekker Inc., NY (1974); and compounds of formula (III) wherein R₀ is is replaced by another substituent such as an alkyl group having 1 to 6 carbon atoms substituted with a halogen atom (e.g. fluorine, chlorine, bromine and bd), a hydroxyl group, a cyano group, an amino group, a heterocyclic group, a silyl group, -CONH, etc. (e.g. 2-chloroethyl, 2-bromoethyl, 2,2,2-trifluoroethyl, 2,3-dibromopropyl, 2-hydroxyethyl, 3-hydroxypropyl, 2,3-dihydroxypropyl, 3-chloro-2-hydroxypropyl, 2-cyanoethyl, 3-(trimethoxysilyl)propyl, 2-furylethyl, 2-thienylethyl, 2-(N-morpholino)ethyl, 2-amidoethyl, 2-methylsulfonylethyl, 2-(N,N-dimethylamino)ethyl and 2-(N,N-diethylamino)ethyl).

Other copolymerization components that can constitute the resin (B) are not limited to the above monomers. Preferably, the proportion of each of these copolymerization components should not exceed 30% by weight, more preferably 20% by weight, of the resin (B).

In particular, when the binder resin contains a heat- and/or light-curable functional group, it is preferred in the present invention to use a reaction accelerator for accelerating crosslinking in the photoconductive layer.

When crosslinking is effected by forming a chemical bond between functional groups, suitable reaction accelerators that can be used include organic acid type crosslinking agents (e.g., acetic acid, propionic acid, butyric acid, benzenesulfonic acid, and p-toluenesulfonic acid). The compounds described in Shinzo Yamashita and Tosuke Kaneko (eds.), Kakyozai Handbook, Taiseisha (1981) can also be used as crosslinking agents. For example, generally used crosslinking agents such as organosilanes, polyurethanes, and polyisocyanates, and curing agents such as epoxy resins and melamine resins can be used.

When crosslinking is effected by a polymerization reaction, suitable reaction accelerators that can be used include polymerization initiators (such as peroxides and azobis compounds, preferably azobis type polymerization initiators) and polyfunctional polymerizable group-containing monomers (e.g. vinyl methacrylate, allyl methacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, divinyl succinic acid ester, divinyl adipic acid ester, diallyl succinic acid ester, 2-methylvinyl methacrylate and divinylbenzene).

When the binder resin contains a photocrosslinkable functional group, a sensitizer, a photopolymerizable monomer and the like may be added. More specifically, compounds described in the above-mentioned literatures concerning the photosensitive resins may be used.

When the binder resin contains a thermosetting functional group, the photoconductive substance-binder resin dispersed system is subjected to a thermosetting treatment. The thermosetting treatment can be carried out by drying the photoconductive coating under conditions more severe than those generally used for the manufacture of conventional photoreceptors. For example, the thermosetting can be achieved by drying the coating at a temperature of 60 to 120°C for 5 to 120 minutes. When the binder resin contains a photosetting functional group, the coating is subjected to a photosetting treatment by applying electron rays, X-rays, UV rays or plasma rays. The photosetting treatment can be effected either during drying or before or after drying. The reaction can be accelerated by using the drying conditions specified above. The use of the above reaction accelerator in combination with the binder resin containing the heat and/or light curing functional group enables the curing to be carried out under milder conditions.

The crosslinking accelerator described above is preferably used in an amount of 1 to 30% by weight, based on the total binder resin.

The resin (B) described above can be used either alone or as a combination of two or more thereof.

The ratio of resin (A) to resin (B) varies depending on the type, particle size and surface condition of the inorganic photoconductive material used. In general, the weight ratio of resin (A) to resin (B) is 5 to 80:95 to 20, preferably 10 to 60:90 to 40.

The inorganic photoconductive material usable in the present invention includes zinc oxide, titanium oxide, zinc sulfide, cadmium sulfide, cadmium carbonate, zinc selenide, cadmium selenide, tellurium selenide and lead sulfide.

The resin binder is used in a total amount of 10 to 100 parts by weight, preferably 15 to 50 parts by weight, per 100 parts by weight of the inorganic photoconductive material.

If desired, the photoconductive layer of the present invention may contain various spectral sensitizers. Examples of suitable spectral sensitizers are carbonium dyes, diphenylmethane dyes, triphenylmethane dyes, xanthene dyes, phthalein dyes, polymethine dyes (e.g., oxonol dyes, merocyanine dyes, cyanine dyes, rhodacyanine dyes, and styryl dyes), phthalocyanine dyes (including metallized dyes), and the like.

Specific examples of suitable carbonium dyes, triphenylmethane dyes, xanthene dyes and phthalein dyes are described in JP-B-51-452, JP-A-50-90334, JP-A-50-114227, JP-A-53-39130, JP-A-53-82353, US Patents 3052540 and 4054450 and in JP-A-57-16456.

Suitable polymethine dyes such as oxonol dyes, merocyanine dyes, cyanine dyes and rhodacyanine dyes include those described in FM Harmmer, The Cyanine Dyes and Related Compounds. Specific examples are described in U.S. Patents 3,047,384, 3,110,591, 3,121,008, 3125447, 3128179, 3132942 and 3622317, British Patents 1226892, 1309274 and 1405898, JP-B-48-7814 and JP-B-55-18892.

In addition, polymethine dyes suitable for spectral sensitization in the longer wavelength range of 700 nm or more, i.e., from the near infrared region to the infrared region, include those described in JP-A-47-840, JP-A-47-44180, JP-B-51-41061, JP-A-49-5034, JP-A-49-45122, JP-A-57-46245, JP-A-56-35141, JP-A-57-157254, JP-A-61-26044, JP-A-61-27551, US Patents 3619154 and 4175956, and Research Disclosure, 216, pp. 117 - 118 (1982).

The photoreceptor of the present invention is particularly excellent in that the performance characteristics are not liable to fluctuate even when combined with various kinds of sensitizing dyes.

If desired, the photoconductive layer may further contain various additives conventionally used in an electrophotographic photoconductive layer, such as chemical sensitizers. Examples of such additives include electron-attracting compounds (e.g., halogen, benzoquinone, chloranil, acid anhydrides, and organic carboxylic acids) described in Imaging, Vol. 1973, No. 8, 5. 12 above; and polyarylalkane compounds, hindered phenol compounds, and p-phenylenediamine compounds described in Hiroshi Komon et al., Saikin-no Kododen Zairyo to Kankotai no Kaihatsu Jitsuyoka, Chap. 4 to 6, Nippon Kagaku Joho K.K. (1986).

The amount of these additives is not particularly critical and is usually in the range of 0.0001 to 2.0 parts by weight per 100 parts by weight of the photoconductive substance.

The photoconductive layer of the photoreceptor suitably has a thickness of 1 to 100 µm, in particular 10 to 50 µm.

When the photoconductive layer functions as a charge generation layer in a laminated photoreceptor comprising a charge generation layer and a charge transport layer, the thickness of the Charge generation layer suitably in the range of 0.01 to 1 µm, in particular 0.05 to 0.5 µm.

The charge transport materials usable in the laminated photoreceptor described above include polyvinylcarbazole, oxazole dyes, pyrazoline dyes and triphenylmethane dyes. The thickness of the charge transport layer is in the range of 5 to 40 µm, preferably 10 to 30 µm.

Resins that can be used in the insulating layer or the charge transport layer typically include thermoplastic and thermosetting resins, e.g. polystyrene resins, polyester resins, cellulose resins, polyether resins, vinyl chloride resins, vinyl acetate resins, vinyl chloride-vinyl acetate copolymer resins, polyacrylate resins, polyolefin resins, urethane resins, epoxy resins, melamine resins and silicone resins.

The photoconductive layer of the present invention can be provided on any known support. In general, a support for an electrophotographic photosensitive layer is preferably electrically conductive. Any conventionally used conductive support can be used in the present invention. Examples of suitable conductive supports include a base, e.g., a metal sheet, paper, synthetic resin film, etc., which has been made electrically conductive, for example, by impregnation with a low-resistance substance; the above-described base whose back surface (opposite to the photosensitive layer side) has been made conductive and which further has at least one layer for preventing curling of the above-described supports and has a water-resistant adhesive layer thereon; the above-described supports having at least one precoat layer thereon; and paper laminated with a synthetic resin film on which aluminum, etc. is deposited.

Concrete examples of conductive carriers and materials for imparting conductivity are described in Yuko Sakamoto, Denshishashi, Volume 14, No. 1, pp. 2 - 11 (1975), Hiroyui Moriga, Nyumon Tokushushi no Kagaku, Kobunshi Kankokai (1975), and MF Hoover, J. Macromol. Sci. Chem., A-4(6), pp. 1327 - 1417 (1970).

The present invention will now be illustrated in more detail by means of Synthesis Examples, Examples and Comparative Examples, but it should be understood that the present invention should not be construed as being limited thereto. Unless otherwise specified herein, all parts, percentages, ratios and the like are by weight.

SYNTHESIS EXAMPLE 1 Synthesis of resin (A-1)

A solution of a mixture of 95 g of 2-chloro-6-methylphenyl acrylate, 150 g of toluene and 50 g of isopropanol was heated to 80°C in a nitrogen stream, and 5 g of 4,4'-azobis(4-cyanovaleric acid) was added thereto to effect polymerization for 10 hours. The resulting resin [referred to as (A-1)] had a weight average molecular weight (hereinafter abbreviated as Mw) of 6500 and the following chemical structure.

SYNTHESIS EXAMPLES 2 TO 23 Synthesis of resins (A-2) to (A-23)

The resins (A) of the following Table 1 were synthesized from the corresponding monomers under the same polymerization conditions as in Synthesis Example 1. These resins had a Mw between 6000 and 8000. TABLE 1 Synthesis example No. Resin (A) No. Ester substituent R TABLE 1 (continued) Synthesis Example No. Resin (A) No. Ester Substituent R TABLE 1 (continued) Synthesis Example No. Resin (A) No. Ester Substituent R TABLE 1 (continued) Synthesis Example No. Resin (A) No. Ester Substituent R

SYNTHESIS EXAMPLE 24 Synthesis of resin (A-24)

A solution of a mixture of 97 g of 2,6-dichlorophenyl methacrylate, 3 g of thioglycolic acid, 150 g of toluene and 50 g of isopropanol was heated to 65°C in a nitrogen stream and 0.8 g of azobisisobutyronitrile was added thereto and the reaction was carried out for 8 hours. The resulting copolymer (A-24) had an Mw of 7800 and the following chemical structure:

SYNTHESIS EXAMPLES 25 TO 35 Synthesis of resins (A-25) to (A-35)

Resins (A) shown in Table 2 below were synthesized under the same polymerization conditions as in Synthesis Example 24, except that thioglycolic acid as used in Synthesis Example 24 was replaced with the compounds shown in Table 2, respectively. The resins had Mw between 7500 and 8500. TABLE 2 Synthesis example No. Resin (A) No. Chain transfer agent TABLE 2 (continued) Synthesis example No. Resin (A) No. Chain transfer agent

SYNTHESIS EXAMPLES 36 TO 46 Synthesis of resins (A-36) to (A-46)

The resins (A) shown in Table 3 were synthesized under the same polymerization conditions as in the previous synthesis examples. TABLE 3 Synthesis Example No. Resin (A) No. TABLE 3 (continued) Synthesis Example No. Resin (A) No.

SYNTHESIS EXAMPLE 47 Synthesis of resin (A-47)

In the same manner as in the foregoing Synthesis Examples, a copolymer (A-31) having a weight average molecular weight of 9500 and the following chemical structure was prepared.

(weight based copolymerization ratio)

SYNTHESIS EXAMPLES 48 TO 53 Synthesis of resins (A-48) to (A-53)

Resins (A) shown in Table 4 below were prepared in the same manner as in Synthesis Example 47. TABLE 4 (Copolymerization ratio: by weight) Synthesis example No. Resin (A) No. Copolymerization component

EXAMPLE 1

A mixture of 6 g (solid basis) of (A-1) prepared in Synthesis Example 1, 34 g (solid basis) of polyethyl methacrylate [Mw: 3.6 x 105; hereinafter referred to as (B-1)], 200 g of zinc oxide, 0.018 g of cyanine dye (A) shown below, 0.30 g of phthalic anhydride and 300 g of toluene was dispersed in a ball mill for 3 hours. The resulting photosensitive composition was coated onto electroconductive paper with a wire bar to a dry thickness of 22 g/m2, followed by drying at 110°C for 30 seconds. The coating was allowed to stand in a dark place at 20°C and 65% RH (relative humidity) for 24 hours to prepare an electrophotographic photoreceptor. Cyanine dye (A):

EXAMPLE 2

An electrophotographic photoreceptor was prepared in the same manner as in Example 1 except that 34 g of (B-1) was replaced by 34 g of (B-2) shown below.

(B-2):

(Mean: 6.5 x 10&sup4;)

(Copolymerization ratio: by weight, as below)

EXAMPLE 3

A mixture of 8 g (A-24), 32 g (B-3) shown below, 200 g of zinc oxide, 0.018 g of cyanine dye (A), 0.30 g of phthalic anhydride and 300 g of toluene was dispersed in a ball mill for 2 hours and 2 g of 1,3-xylylene diisocyanate was added thereto, followed by dispersion in a ball mill for 10 minutes. The resulting composition was coated on electroconductive paper with a wire rod to a dry thickness of 22 gim and dried at 100°C for 12 seconds and then at 120°C for 2 hours. Thereafter, the coating was left to stand in a dark place at 20°C and 65% RH for 24 hours to obtain an electrophotographic photoreceptor.

(B-3):

(Mean: 5.6 x 10&sup4;)

COMPARISON EXAMPLE A

An electrophotographic photoreceptor (referred to as Sample A) was prepared in the same manner as in Example 1, except that 6 g of (A-1) was replaced by 6 g of (R-1) shown below.

(R-1):

(mean: 7.6 x 10³)

COMPARISON EXAMPLE B

An electrophotographic photoreceptor (sample B) was prepared in the same manner as in Example 1, except that (A-1) and (B-1) were replaced by 40 g of (B-2) as used in Example 2.

The film properties of each of the photoreceptors obtained in Examples 1 to 3 and Comparative Examples A and B were evaluated in terms of surface smoothness and mechanical strength; electrostatic properties; image forming performance; oil desensitizability when used as an offset master plate precursor (expressed as a contact angle with water after the oil desensitization treatment); and printing durability when used as an offset master plate according to the following test methods. The results obtained are shown in Table 5 below:

1) Smoothness of the photoconductive layer:

The smoothness (sec/cm³) was measured using a Beck smoothness tester manufactured by Kumagaya Riko K.K. under the condition of an air volume of 1 cm³.

2) Mechanical strength of the photoconductive layer:

The surface of the photoreceptor was repeatedly rubbed with abrasive paper (#1000) under a load of 50 g/cm using a surface tester (Heidon Model 14, manufactured by Shinto Kagaku K.K.). After dusting, the abrasion loss of the photoconductive layer was measured to obtain the film retention (%).

3) Electrostatic properties:

The sample was charged with a corona discharge to a voltage of -6 kV using a paper analyzer ("Paper Analyzer SP-428", manufactured by Kawaguchi Denki KK) for 20 seconds in a dark room at 20ºC and 65% RH. 10 seconds after corona discharge, the surface potential V₁₀₋ was measured. The sample was left in the dark for a further 120 seconds and the potential V₁₃₋ was measured. The dark decay retention (DRR; %), i.e. the percentage retention of the potential after a 120 second dark decay, was calculated from the following:

DRR (%) = (V₁₃�0/V₁�0) x 100

Separately, the sample was charged to -400 V with a corona discharge and then exposed to light emitted from a gallium aluminum arsenic semiconductor laser (oscillation wavelength: 780 nm), and the time required for the surface potential V₁₀ to drop to one tenth was measured to obtain an exposure E₁₁₁₀₀ (erg/cm2).

The measurements were carried out under the conditions of 20ºC and 65% RH (hereinafter referred to as Condition I) or 30ºC and 80% RH (hereinafter referred to as Condition II).

4) Image generation behavior:

After the samples were left to stand for one day at 20ºC and 65% RH (Condition 1) or at 30ºC and 80% RH (Condition II), each sample was charged to -6 kV and exposed to light emitted from a gallium aluminum arsenic semiconductor laser (oscillation wavelength: 780 nm; power: 2.8 mW) in an exposure amount of 56 erg/cm² (on the surface of the photoconductive layer) at a distance of 25 µm and a scanning speed of 280 m/sec. The electrostatic latent image was developed with a liquid developer ("ELP-T", manufactured by Fuji Photo Film Co., Ltd), followed by fixing. The reproduced image was visually evaluated for fog and image quality.

5) Contact angle with water:

The sample was prepared once by an etching processing device using an oil desensitizing solution ("ELP-E", by Fuji Photo Film Co., Ltd.) to make the surface of the photoconductive layer oil-desensitized. On the thus oil-desensitized surface, a drop of 2 µl of distilled water was placed and the contact angle formed between the surface and the water was measured using a goniometer.

6) Print durability:

The sample was processed in the same manner as described in 4) above, and the surface of the photoconductive layer was subjected to oil desensitization under the same conditions as in 5) above. The resulting planographic printing plate was attached to an offset printing machine ("Oliver Model 52", manufactured by Sakura Seisakusho KK), and printing was carried out on fine paper. The number of prints obtained until background stains appeared in the non-image areas or until the quality of the image areas deteriorated was taken as the print durability. The greater the number of prints, the higher the print durability. TABLE 5 Example Comparative example Surface smoothness Film strength Electrostatic properties Condition Image forming behavior: Contact angle with water Printing durability Good or less Not good (scratching of fine letters or lines) or more Poor (cutting off of fine letters or lines) Extremely poor (cutting off of fine letters or lines) Background stains from the start of printing

As is apparent from the results in Table 5, each of the photoreceptors of the present invention exhibited satisfactory surface smoothness and electrostatic properties. When each photoreceptor was used as an offset master plate precursor, the reproduced image was clear and free from background stains in the non-image area. Without wishing to be bound by this, these results appear to be due to the sufficient adsorption of the binder resin to the photoconductive substance and the sufficient coverage of the surface of the photoconductive particles with the binder resin. For the same reason, oil-desensitization of the offset master plate precursor with an oil-desensitizing solution was sufficient to make the non-image area sufficiently hydrophilic as shown by the small contact angle of 15° or less with water. In practical printing using the resulting master plate, no background stains were observed on the prints.

Furthermore, the photoconductive layer of each photoreceptor according to the invention had a film strength of 88% or more and when used as an offset master plate, it provided more than 8000 prints with clear images free from background stains.

These results demonstrate that the film strength can be significantly improved by the action of resin (A) in combination with resin (B) or in combination with resin (B) and a crosslinking agent without deteriorating the effects of resin (A).

Sample A, in which a low molecular weight copolymer resin comprising an alkyl methacrylate unit and an acidic group-containing unit was used, showed considerable improvements in electrostatic properties over Sample B, in which only a conventionally known binder resin was used, but was inferior in properties to the samples of the present invention. In fact, when Sample A was processed using a low-power semiconductor laser at a reduced scanning speed, the reproduced image was found to be of insufficient quality.

Printing was carried out using an offset master plate made of Sample A or B. As a result, cut-off thin lines or fine letters were formed on the precursor for the plate of Sample A from about 500th print due to the unsatisfactory reproduction of the image. Serious background stains were observed right from the start of printing due to the electrostatic properties being so poor for the plate of Sample B.

From all these considerations, it is thus clear that an electrophotographic photoreceptor satisfying the two requirements of electrostatic properties and suitability for printing cannot be obtained without the binder resin of the present invention.

EXAMPLES 4 TO 12

An electrophotographic photoreceptor was prepared in the same manner as in Example 1, except that 6 g of (A-1) and 34 g of (B-1) were replaced by the resins (A) and (B) shown in Table 6, respectively, and the cyanine dye (A) was replaced by 0.020 g of the cyanine dye (B) shown below. Cyanine dye (B):

The behavioral characteristics of the resulting photoreceptors were evaluated in the same manner as in Example 1, and the results obtained are shown in the following Table 6. The electrostatic characteristics in Table 6 are those determined under Condition II (30 °C, 80% RH). TABLE 6 Example No. Resin Electrostatic properties (Condition II) Polybutyl methacrylate Styrene/ethyl methacrylate copolymer Polypropyl methacrylate Ethyl methacrylate/acrylonitrile copolymer Polybenzyl methacrylate Methyl methacrylate/methacrylate Ethyl methacrylate/2-cyanoethyl methacrylate Styrene/butyl methacrylate copolymer Methyl methacrylate/ethyl methacrylate

From the results in Table 6, it is apparent that each of the photoreceptors of the present invention had excellent charging characteristics, dark decay retention and photosensitivity and provided a clear reproduced image even when processed under severe conditions of high temperature and high humidity (30°C, 80% RH). An offset master plate made from the photoreceptor of the present invention provided more than 8,000 prints with a clear image without background stains.

EXAMPLES 13 TO 20

An electrophotographic photoreceptor was prepared in the same manner as in Example 3, except that 6 g of (A-24), 32 g of (B-3) were replaced by the same amount of the resins (A) and (B) shown in Table 7 below, respectively, and 2 g of 1,3-xylylene diisocyanate (crosslinking agent) was replaced by the specified amount of the crosslinking agent shown in Table 7 below. TABLE 7 Example No. Resin Crosslinking agent 1,3-Xylylene diisocyanate 1,6-Hexamethylenediamine Terephthalic acid 1,4-Tetramethylenediamine TABLE 7 (continued) Example No. Resin Crosslinking Agent Polyethylene glycol Polypropylene glycol 1,2-hexamethylene diisocyanate Ethylene glycol dimethacrylate

The electrostatic properties and printing properties of each of the resulting photoreceptors were evaluated in the same manner as in Example 1. As a result, it was proved that the photoreceptors of the present invention had excellent charging properties, excellent dark decay retention and excellent photosensitivity and provided a clear reproduced image free from background fog or cut-off thin lines even when processed under severe conditions of high temperature and high humidity (30°C, 80% RH). When used as an offset master plate precursor, the resulting printing plates provided more than 10,000 prints with a clear image free from background stains in the non-image area.

EXAMPLES 21 TO 24

A mixture of 6.5 g each of the resins (A) shown in Table 8 below, 20 g each of the resins (B) having group X shown in Table 8 below, 200 g of zinc oxide, 0.018 of methine dye (C) shown below, 0.35 g of maleic anhydride and 300 g of toluene was dispersed in a ball mill for 3 hours. To the dispersion was added 13.5 g each of the resins (B) having group Y shown in Table 8 below, followed by further dispersing in a ball mill for 10 minutes. The resulting photoconductive composition was coated onto conductive paper with a wire bar in a dry thickness of 20 g/m² and heated at 100°C for 15 seconds and then at 120°C for 2 hours. Then, the resulting coated material was allowed to stand at 20 °C and 65% RH for 24 hours to obtain an electrophotographic photoreceptor. Methine dye (C): TABLE 8 Example No. Resin Group

As a result of evaluations in the same manner as in Example 1, it was found that each of the resulting photoreceptors according to the present invention had excellent charging characteristics, excellent dark decay retention and excellent photosensitivity and provided a clear reproduced image free from background fog even when processed under severe conditions of high temperature and high humidity (30°C, 80% RH).

When an offset printing plate made from each of the photoreceptors of the present invention was used as an offset stencil for printing, more than 10,000 prints with a clear image could be obtained.

EXAMPLE 25

A mixture of 7 g of (A-27), 18 g of (B-15), 200 g of zinc oxide, 0.50 g of diodeosine, 0.25 g of tetrabromophenol blue, 0.30 g of uranine, 0.30 g of tetrahydrophthalic anhydride and 240 g of toluene was dispersed in a ball mill for 2 hours. To the dispersion was further added 15 g of resin (B-26) shown below, followed by dispersing for 10 minutes. The resulting photosensitive composition was coated onto conductive paper with a wire bar in a dry thickness of 20 g/m, followed by drying at 110°C for 30 seconds and then at 120°C for 2 hours. The coating was allowed to stand at 20°C and 65% RH for 24 hours in a dark place to prepare an electrophotographic photoreceptor. Resin (B-26)

(Mean: 3.0 x 10&sup4;)

The resulting photoreceptor was evaluated in the same manner as in Example 1 with the following exceptions. In the evaluation of electrostatic properties, DRR (%) was calculated from the formula (V₇₀/V₁₀ x 100), where V₁₀ and V₇₀ are surface potentials determined after standing for 10 seconds and 70 seconds after the termination of corona discharge, respectively. The photosensitivity was determined using visible light (2.0 lux) for exposure. In the evaluation of image forming performance, the sample was processed as a printing plate precursor to form a toner image using an automatic plate making machine "ELP 404V" (manufactured by Fuji Photo Film Co., Ltd.) using "ELP-T" (manufactured by Fuji Photo Film Co., Ltd.) as a toner.

The results obtained were as follows.

Surface smoothness: 120 cm³/sec.

Film strength: 93%

Electrostatic properties: V₁₀(V) DRR (%) E1/10 (lux.sec.) Condition I (20ºC, 65% RH) Condition II (30ºC, 80% RH)

Image generation behavior:

A satisfactory reproduced image was produced under both Condition I and Condition II. Print durability: 10,000 prints

Thus, it is apparent that the photoreceptor of the present invention exhibits excellent electrophotographic properties and high printing durability.

EXAMPLES 26 AND 27

A mixture of 6 g each of (A-34) and (A-20), 34 g each of the resins (B) shown in Table 9 below, 200 g zinc oxide, 0.02 g uranine, 0.04 g diodeosine, 0.03 9 bromophenol blue, 0.40 g of phthalic anhydride and 300 g of toluene were dispersed in a ball mill for 2 hours. The resulting composition was coated onto conductive paper with a wire rod in a dry thickness of 20 g/m² and dried at 110°C for 1 minute. Then, the coating was exposed to light emitted from a high pressure mercury lamp over the entire surface thereof for 3 minutes and then left to stand in a dark place at 20°C and 65% RH for 24 hours to prepare an electrophotographic photoreceptor. The properties of the resulting photoreceptors are shown in Table 10 below. TABLE 9 Example No. Resin TABLE 10 Example No. Surface Smoothness Film Strength Print Durability

As shown by the results in Table 10, the photoreceptors of the present invention had excellent charging characteristics, excellent dark decay retention and excellent photosensitivity, and provided a clear reproduced image free from background fog even when processed under severe conditions of high temperature and high humidity (30°C, 80% RH). When used as an offset master plate precursor, the resulting master plate provided 8,500 to 9,000 prints of clear image.

Claims (11)

1. An electrophotographic photoreceptor comprising a support having thereon at least one photoconductive layer containing at least inorganic photoconductive particles and a binder resin, said binder resin having a weight average molecular weight of 1 x 10³ to 5 x 10⁴, and comprising (A) at least one resin containing as a polymerization component not less than 30% by weight of at least one repeating unit (ai) represented by the formula (I) or (II): wherein X₁ and X, which may be the same or different, each represent a hydrogen atom, a hydrocarbon group having 1 to 10 carbon atoms, a chlorine atom, a bromine atom, -COY₁ or -COOY, Y₁ and Y each represent a hydrocarbon group having 1 to 10 carbon atoms, with the proviso that X₁ and X cannot both simultaneously represent hydrogen; and W₁ and W each represent a bond or a linking group containing 1 to 4 linking atoms which links -COO- and the benzene ring, at least one acidic group consisting of (i) -PO₃H, (ii) -SO₃H, (iii) -COOH, (iv) - -OH, wherein R represents a hydrocarbon group having 1 to 10 carbon atoms or -OR', wherein R' represents a hydrocarbon group having 1 to 10 carbon atoms, and (v) a cyclic acid anhydride containing group is bonded to only one of the terminals of the polymer main chain thereof. 2. An electrophotographic photoreceptor according to claim 1, in which the resin (A) further comprises 1 to 20% by weight of at least one repeating unit (a-ii) containing a heat- and/or photo-curable functional group. 3. An electrophotographic photoreceptor according to claim 1 or 2, wherein the binder resin further comprises (B) at least one resin having a weight average molecular weight of 2 x 10⁴ to 6 x 10⁵. 4. An electrophotographic photoreceptor according to claim 3, wherein the resin (B) comprises at least 30% by weight of a repeating unit (bi) represented by the formula (III): wherein a1 and a, which may be the same or different, each represent a hydrogen atom, a halogen atom, a cyano group or a hydrocarbon group; and R0 represents a hydrocarbon group. 5. An electrophotographic photoreceptor according to claim 4, in which the resin (B) further comprises 0.05 to 5% by weight of a copolymerization component containing at least one acidic group selected from (i) -PO₃H, (ii) -SO₃H, (iii) -COOH, (iv) - -OH, wherein R represents a hydrocarbon group having 1 to 10 carbon atoms or -OR-, where R' represents a hydrocarbon group having 1 to 10 carbon atoms, and (v) a cyclic acid anhydride-containing group, wherein the resin (B) has a weight average molecular weight of 2 x 10⁴ to 1 x 10⁵. 6. An electrophotographic photoreceptor according to any one of claims 3 to 5, in which the resin (B) comprises 1 to 30% by weight of at least one repeating unit containing a heat- and/or photo-curing functional group. 7. An electrophotographic photoreceptor according to any one of claims 1 to 6, in which the photoconductive layer further contains a heat- and/or light-curing crosslinking agent. 8. An electrophotographic photoreceptor according to any one of claims 1 to 7, in which X₁ and X each represent a hydrogen atom, a chlorine atom, a bromine atom, an alkyl group having up to 4 carbon atoms, an aralkyl group having 7 to 9 carbon atoms, an aryl group, or -COY₁ or -COOY, wherein Y₁ and Y each represent the groups described for X₁ and X, except that X₁ and X do not simultaneously represent a hydrogen atom; W represents a bond or a 1 to 4 connecting atoms and W has the same meaning as W₁. 9. An electrophotographic photoreceptor according to any one of claims 1 to 8, in which the hydrocarbon group represented by R or R' is an aliphatic group having 1 to 10 carbon atoms or an aryl group. 10. An electrophotographic photoreceptor according to any one of claims 1 to 9, in which the acid anhydride-containing group is an aliphatic dicarboxylic anhydride ring or an aromatic dicarboxylic anhydride ring. 11. An electrophotographic photoreceptor according to claim 10, in which the aliphatic dicarboxylic anhydride ring is a succinic anhydride ring, a glutaconic anhydride ring, a maleic anhydride ring, a cyclopentane-1,2-dicarboxylic anhydride ring, a cyclohexane-1,2-dicarboxylic anhydride ring, a cyclohexene-1,2-dicarboxylic anhydride ring or a 2,3-bicyclo [2.2.2] octanedicarboxylic anhydride ring, which rings may be unsubstituted or substituted with at least one group selected from a halogen atom and an alkyl group, and the aromatic dicarboxylic anhydride ring is a phthalic anhydride ring, a naphthalenedicarboxylic anhydride ring, a pyridinedicarboxylic anhydride ring or a thiophenedicarboxylic anhydride ring which may be unsubstituted or substituted with at least one group selected from a halogen atom, an alkyl group, a hydroxyl group, a cyano group, a nitro group and an alkoxycarbonyl group.